Buffett told business television network CNBC his investment amounts to about 64 million shares, the equivalent of a 5.5 per cent stake.

The investment would make Berkshire Hathaway IBM's largest or second-largest shareholder - investment advisory group State Street holds more than 64 million shares.

Known as the Sage of Omaha for his investing skills, the 81-year-old Buffett told CNBC Berkshire had paid an average price of $US170 a share, 10 per cent lower than last Friday's closing price of $US187.38.

Buffett said in the TV interview Berkshire had finished its IBM spree and he did not intend to buy more of the company.

"I wouldn't be talking about it if I did."

Buffett praised IBM, which celebrated its 100th anniversary in June, for having a strong plan for the future, saying: "They've done all kinds of things right."

In late October, IBM named Virginia Rometty, the current head of sales, marketing and strategy, to take over as chief executive on January 1, making her the first woman to lead the iconic US firm.

Buffett's stock-picking prowess has made him the world's third-richest man, with a fortune of $US50 billion, according to Forbes magazine's latest list of the world's billionaires.

Buffett also said Berkshire had increased its holdings in a leading US bank, Wells Fargo, but did not give any figures.